Arboreal Mammals Research Articles

A New and Simple Method to Capture Small Arboreal Mammals: The Suspended Pitfall

The suspended pitfall demonstrates a new and simple mechanism to capture small arboreal and scansorial mammals. It is an arboreal version of the pitfalls traditionally used to capture terrestrial amphibians and reptiles. Buckets with bait inside are raised by a rope until they reach a tree branch at the desired height. Tests were performed in the Atlantic Forest at three different sites at the mouth of Doce River in Linhares, southeastern Brazil. In one of them suspended pitfalls were set up in the understory of a shaded cacao plantation (cabruca agroforest) in the branches of cacao trees between 2 and 3 m in height, and in the other they were placed in a native forest between 5 to 15 m in height. At the third site, suspended pitfalls were tested together with the other live traps used hitherto in the understory of other cabruca agroforest. The marsupials Didelphis aurita, Caluromys philander, Marmosa (Micoureus) paraguayana, Gracilinanus microtarsus, Marmosa murina and the rodent Rhipidomys mastacalis were captured by suspended pitfall. This live trap was capable of catching all sizes of small arboreal mammals, including juvenile individuals. This method proved to be functional for the capture of some small arboreal mammals and may be a complementary alternative for sampling in high forest strata.

Landscape management of the mahogany glider (Petaurus gracilis) across its distribution: subpopulations and corridor priorities

Key threatening processes to biodiversity include habitat loss and fragmentation, with populations restricted to small fragments of habitat being more prone to extinction. The mahogany glider (Petaurus gracilis) is endemic to sclerophyll woodland forests between Tully and Ingham in north Queensland and is one of Australia’s most endangered arboreal mammals due to these processes. The aim of this study was to identify the degree of habitat fragmentation of the remaining remnant vegetation of the mahogany glider, identify subpopulations within its distribution and identify key wildlife corridors for restoration to facilitate the movement of this species within and between subpopulations. Ten glider subpopulations, spread over 998 habitat fragments, were identified, of which only five subpopulations may currently be considered to be viable. To assist in providing habitat connectivity between and within the subpopulations, 55 corridors were identified for restoration that had an average length of 8.25 km. The average number of gaps greater than 30 m was 3.4 per corridor, with the average length of these gaps being 523 m. This study confirmed a high degree of habitat fragmentation across the distribution of the mahogany glider and highlighted the need to strengthen the remaining subpopulations by restoring habitat connectivity between the remaining habitat fragments.

Contrasting patterns of decline in two arboreal marsupials from Northern Australia

Widespread declines of small- to medium-sized, semi-arboreal mammals in the drier regions of Northern Australia are of global concern. These declines have been variously attributed to either disruption of available resources or increased predation pressure. We aimed to clarify causes of mammal decline in Northern Australia using a comparative methods approach, examining historical changes in the distribution of two arboreal mammals, the common brushtail possum (Trichosurus vulpecula) and the savanna glider (Petaurus ariel), and model drivers of their current abundance. We used single-season occupancy models to describe changes in the geographic range of P. ariel and T. vulpecula based on multiple-source occurrence data, from before and after 1993. We conducted spotlighting surveys in 2016 across the mesic savannas of the Northern Territory to identify environmental correlates of the current abundance of each species. Our results show that, within northwestern Australia, the geographic range (area where the probability of occupancy was ≥ 5%) has declined by 72% for T. vulpecula and 35% for P. ariel, between the historical and contemporary periods (before and after 1993, respectively). The abundance of each species varied substantially across the study area, but high T. vulpecula abundance was associated with high shrub density. We propose that areas with high shrub density are providing refuge for T. vulpecula, due to an increase in protection from predation by feral cats (Felis catus). Regardless of the driver, conservation management within Northern Australia should concentrate efforts on maintaining or increasing shrub abundance in tropical savannas. Our findings should also be viewed as an indicator of early stages of P. ariel decline and prompt targeted monitoring efforts.

Needing a drink: Rainfall and temperature drive the use of free water by a threatened arboreal folivore.

Arboreal folivores are particularly vulnerable to the impacts of extreme climate change-driven heatwaves and droughts as they rely on leaf moisture to maintain hydration. During these increasingly frequent and intense weather events, leaf water content may not be enough to meet their moisture requirements, potentially leading to large-scale mortality due to dehydration. Water supplementation could be critical for the conservation of these animals. We tested artificial water stations for a threatened arboreal folivore, the koala (Phascolarctos cinereus), as a potential mitigation measure during hot and dry weather in New South Wales, Australia. We provided ground and tree drinkers to koalas and investigated changes in use with season, environmental conditions and foliar moisture. Our study provides first evidence of the regular use of free water by koalas. Koalas used supplemented water extensively throughout the year, even during cooler months. Time spent drinking varied with season and depended on days since last rain and temperature. The more days without rain, the more time koalas spent drinking. When temperature was high, visits to water stations were more frequent, indicating that in hot weather koalas need regular access to free water. Our results suggest that future changes in rainfall regimes and temperature in Australia have the potential to critically affect koala populations. Our conclusions can be applied to many other arboreal folivorous mammals worldwide which rely on leaves for their nutritional and water requirements. Artificial water stations may facilitate the resilience of vulnerable arboreal folivores during heat and drought events and may help mitigate the effects of climate change.

Human disturbance impacts on rainforest mammals are most notable in the canopy, especially for larger‐bodied species

AbstractAimCommunity‐level assessments of how biodiversity responds to disturbance within forest habitats are often biased towards terrestrial‐based surveys. However, recent research suggests that arboreal communities of several indicator groups (ants, amphibians, beetles and butterflies) are more susceptible to human disturbance than their terrestrial counterparts, but what about wildlife at higher trophic levels? We assess responses to disturbance, from forest floor to canopy, of a key conservation flagship group: medium to large rainforest mammals.LocationThe Manu Biosphere Reserve, southeast Peru.MethodsWe deploy both arboreal and terrestrial camera traps to directly compare the response of arboreal and terrestrial mammal communities to rainforest degradation and disturbance.ResultsWe show that the arboreal mammal community is more susceptible to habitat disturbance than the terrestrial community. Furthermore, the largest‐bodied arboreal species, which are major seed dispersers, showed the greatest negative response to forest disturbance. The strongest predictors of occupancy probability for arboreal communities were focal tree connectivity and canopy cover, whereas surrounding forest loss and canopy height were there strongest predictors of terrestrial community occupancy, although these also had effects similar in size and magnitude on the arboreal community.Main conclusionsConservation conclusions drawn from camera‐based studies focused on the terrestrial realm likely underestimate the impact of rainforest degradation to arboreal communities and on arboreal rainforest biodiversity in general. We highlight the importance of implementing arboreal research methods, capable of investigating conservation implications of anthropogenic disturbance across all vertical strata, for accurate conservation assessments and improving rainforest management and restoration strategies.

Fruit Predation and Adaptive Strategies of <i>Garcinia imberti</i>, an Endangered Species of Southern Western Ghats

The germination and seedling emergence capacity of partially predated seeds of Garcinia imberti Bourd., an endemic and endangered tree species of the southern Western Ghats, was assessed with differentially devoured seeds. Pre-dispersal, fruit/seed predation by arboreal mammals especially Ratufa indica (Malabar Giant Squirrel) and to a smaller extent by Trachypithecus johnii (Nilgiri Langur) was observed. The fragmented seeds of natural predation as well as manually cut seed pieces showed speedy germination. Seed fragments with more than 50% of seed tissues showed high seed vigour index. The germination behaviour of cut seeds indirectly conveyed the simulated effect of predated seed germination in natural habitat. Germination of fragmented seeds overcomes the inevitable prolific predatory problems by frugivores. This study showed that G. imberti seeds tolerate predation to a certain extent as an adaptive character ensuring seed dispersal and seedling establishment through a unique plant–animal mutuality.

The secret life of possums: data loggers reveal the movement ecology of an arboreal mammal

Understanding animal movement patterns is fundamental to ecology, as it allows inference about species' habitat preferences and their niches. Such knowledge also underpins our ability to predict how animals may respond to environmental change, including habitat loss and modification. Data-logging devices such as GPS trackers and accelerometers are rapidly becoming cheaper and smaller, allowing movement at fine scales to be recorded on a broad range of animal species. We examined movement patterns of an arboreal mammal (bobuck, Trichosurus cunninghami) in a highly fragmented forest ecosystem. The GPS data showed males travelled greater distances than females in linear roadside strip habitats, but not in forest fragments. The accelerometer data showed that both sexes exhibited higher activity levels in roadside habitats compared to forest fragments. By coupling GPS and accelerometer data, we uncovered for this species an ecological pattern similar to other mammals: that male bobucks had higher activity levels than females for a given distance travelled. Our findings also suggest that habitat fragmentation changes the amount and type of activity bobucks perform while moving, and that linear forest strips could be considered “energetically challenging” habitats, which informs how we should manage the spatial distribution of key supplementary resources for this species such as nest sites and minimum fragment sizes.

Hot monkey, cold reality: surveying rainforest canopy mammals using drone-mounted thermal infrared sensors

ABSTRACTAnimals of the rainforest canopies are often endangered by deforestation or hunting but are difficult to survey and study because of the inaccessibility of the treetops, combined with the visual camouflage of many species. Drone-based thermal sensors have the potential to overcome these hurdles by rapidly scanning large forested areas from above, detecting and mapping wildlife based on the contrast between their warm body temperatures and the cool tree canopies. We tested this concept by flying a drone-mounted thermal infrared radiometric sensor over the wildlife-rich rainforests of Barro Colorado Island, Panama. Arboreal mammals had body temperatures around 27°C and were conspicuous in the thermal infrared imagery at night and early morning when the forest canopy was cool (23–25°C), but were difficult to detect by mid-morning, by which time the direct sunshine had heated up canopy vegetation to over 30°C. Species were difficult to identify from thermal infrared imagery alone, but could be recognized from synchronized visual images taken during the daytime. Simultaneous drone and ground-based surveys of the same area proved that the aerial thermal camera did detect high-canopy species missed by the terrestrial observer, but that substantially more animals were detected by the human than by the drone. Because animal detection was so much better at night, when species ID was difficult, we suggest that future work could combine automated detection of animals from thermal infrared imagery with flash photography or IR illumination to enable species ID during nocturnal surveys. We conclude by discussing various logistical challenges that limit the utility of drone-based thermal infrared today, but that could be overcome by continued improvement of technology and collaboration with permitting agencies.

Contemporary breeding biology of critically endangered Regent Honeyeaters: implications for conservation

Identifying factors influencing the demographics of threatened species is essential for conservation, but a lack of comprehensive demographic data often impedes the effective conservation of rare and mobile species. We monitored breeding of critically endangered and semi‐nomadic Regent Honeyeaters Anthochaera phrygia (global population c. 100 pairs) over 3 years throughout their range. Overall nest success probability (0.317) was highly spatially variable and considerably lower than previous estimates for this (and many other honeyeater) species, as was productivity of successful nests (mean 1.58 juveniles fledged). Nest surveillance revealed high predation rates by a range of birds and arboreal mammals as the primary cause of nest failure. An estimated 12% of pairs either failed to establish a territory or their nests did not reach the egg stage. We also found a male bias to the adult sex ratio, with an estimated 1.18 males per female. Juvenile survival for the first 2 weeks after fledging was high (86%). Management interventions that aim to increase nest success in areas of low nest survival must be investigated to address an apparent decline in reproductive output and avoid extinction of the Regent Honeyeater. We show that temporal and spatial variation in the breeding success of rare and highly mobile species can be quantified with robust population monitoring using sampling regimens that account for their life histories. Understanding the causes of spatio‐temporal variation in breeding success can enhance conservation outcomes for such species through spatially and temporally targeted recovery actions.

Comparative Phylogeography of Forest-Dependent Mammals Reveals Paleo-Forest Corridors throughout Sundaland.

The evolutionary history of the colugo, a gliding arboreal mammal distributed throughout Sundaland, was influenced by the location of and connections between forest habitats. By comparing colugo phylogenetic patterns, species ecology, sample distributions, and times of divergence to those of other Sundaic taxa with different life-history traits and dispersal capabilities, we inferred the probable distribution of paleo-forest corridors and their influence on observed biogeographic patterns. We identified a consistent pattern of early diversification between east and west Bornean lineages in colugos, lesser mouse deer, and Sunda pangolins, but not in greater mouse deer. This deep east-west split within Borneo has not been commonly described in mammals. Colugos on West Borneo diverged from colugos in Peninsular Malaysia and Sumatra in the late Pliocene, however most other mammalian populations distributed across these same geographic regions diverged from a common ancestor more recently in the Pleistocene. Low genetic divergence between colugos on large landmasses and their neighboring satellite islands indicated that past forest distributions were recently much larger than present refugial distributions. Our analysis of colugo evolutionary history reconstructs Borneo as the most likely ancestral area of origin for Sunda colugos, and suggests that forests present during the middle Pliocene within the Sunda Shelf were more evergreen and contiguous, while forests were more fragmented, transient, seasonal, or with lower density canopies in the Pleistocene.

Outcomes of decades long installation of nest boxes for arboreal mammals in southern Australia

SummaryNest boxes are commonly installed to support hollow‐using species where the abundance of hollow‐bearing trees is deficient. Recent studies have provided equivocal evidence about the effectiveness of nest box projects and have highlighted significant management costs associated with some projects. We document the functionality of 303 nest boxes installed across five different community‐led projects in southern Australia for periods of 10–25 years. As expected, we found that nest boxes lost functionality over time. However, 60% remained functional to support the Brush‐tailed Phascogale (Phascogale tapoatafa) and the Sugar Glider (Petaurus breviceps) after almost 20 years. Years installed, method of nest box attachment and tree species influenced whether boxes remained functional. Nest box construction material changed over time so could not be assessed specifically. When inspected in a single year, the Brush‐tailed Phascogale occupied 9% of functional boxes and another 48% contained their nests. The Sugar Glider occupied 15% of functional boxes and another 22% contained their nests. These values suggest the nest box installations were highly effective for these species, although more detailed study is needed to understand what contribution these installations have made to support the local populations. Maintenance of most nest boxes occurred twice a year in the first five years after installation, but many received no maintenance for periods of three years, and some 10–15 years, before our census. Our findings suggest that infrequent maintenance by community groups can sustain nest box projects over periods of several decades. Research into employing nest boxes as a management tool in Australia is still in its infancy. Further studies are needed to resolve factors that limit their effectiveness.

Digging the compromise: investigating the link between limb bone histology and fossoriality in the aardvark (Orycteropus afer).

Bone microstructure has long been known as a powerful tool to investigate lifestyle-related biomechanical constraints, and many studies have focused on identifying such constraints in the limb bones of aquatic or arboreal mammals in recent years. The limb bone microstructure of fossorial mammals, however, has not been extensively described. Furthermore, so far, studies on this subject have always focused on the bone histology of small burrowers, such as subterranean rodents or true moles. Physiological constraints associated with digging, however, are known to be strongly influenced by body size, and larger burrowers are likely to exhibit a histological profile more conspicuously influenced by fossorial activity. Here, we describe for the first time the limb bone histology of the aardvark (Orycteropus afer), the largest extant burrowing mammal. The general pattern is very similar for all six sampled limb bones (i.e., humerus, radius, ulna, femur, tibia, and fibula). Most of the cortex at midshaft is comprised of compacted coarse cancellous bone (CCCB), an endosteal tissue formed in the metaphyses through the compaction of bony trabeculae. Conversely, the periosteal bone is highly resorbed in all sections, and is reduced to a thin outer layer, suggesting a pattern of strong cortical drift. This pattern contrasts with that of most large mammals, in which cortical bone is of mostly periosteal origin, and CCCB, being a very compliant bone tissue type, is usually resorbed or remodeled during ontogeny. The link between histology and muscle attachment sites, as well as the influence of the semi-arid environment and ant-eating habits of the aardvark on its bone microstructure, are discussed. We hypothesize that the unusual histological profile of the aardvark is likely the outcome of physiological constraints due to both extensive digging behavior and strong metabolic restrictions. Adaptations to fossoriality are thus the result of a physiological compromise between limited food availability, an environment with high temperature variability, and the need for biomechanical resistance during digging. These results highlight the difficulties of deciphering all factors potentially involved in bone formation in fossorial mammals. Even though the formation and maintaining of CCCB through ontogeny in the aardvark cannot be unambiguously linked with its fossorial habits, a high amount of CCCB has been observed in the limb bones of other large burrowing mammals. The inclusion of such large burrowers in future histological studies is thus likely to improve our understanding of the functional link between bone growth and fossorial lifestyle in an evolutionary context.

Foot postures and grasping of free-ranging Sunda colugos (Galeopterus variegatus) in West Java, Indonesia

Colugos (order Dermoptera) are medium-sized nocturnal arboreal eutherian euarchontan mammals, which glide, climb vertically and hang from different arboreal substrates in the rainforests of Southeast Asia. Their close phylogenetic position to either Primates (as Primatomorpha) or Scandentia (as Sundatheria) renders them significant for understanding evolutionary-adaptive trends of key features within the Euarchonta (primates, scandentia, dermoptera, and plesiadapiformes). In this context, we studied foot positional, postural, and grasping patterns in relation to substrate use in free-ranging Sunda colugos (Galeopterus variegatus) in west Java, Indonesia. On large, strongly inclined substrates, colugos primarily used claw climbing and clinging activities, with a dorsiflexed, abducted, and everted foot using an abducted clawed grasp and abducted hallux. On small, less inclined substrates, colugos habitually used suspensory locomotion and postures with pedal plantarflexion, adduction, inversion, and an adducted clawed grasp and adducted hallux. The morphofunctional similarity of the colugo foot with that of early euarchontans suggests comparable behaviors at the base of euarchontan evolution. Furthermore, the functional-adaptive significance of these behaviors is further investigated under different phylogenetic scenarios, linking dermopterans to either scandentians or primates. Our findings underscore the importance of similar behavioral studies for examining functional-adaptive evolutionary scenarios.

Motion analysis of non-model organisms using a hierarchical model: Influence of setup enclosure dimensions on gait parameters of Swinhoe’s striped squirrels as a test case

In in-vivo motion analyses, data from a limited number of subjects and trials is used as proxy for locomotion properties of entire populations, yet the inherent hierarchy of the individual and population level is usually not accounted for. Despite the increasing availability of hierarchical model frameworks for statistical analyses, they have not been applied extensively to comparative motion analysis. As a case study for the use of hierarchical models, we analyzed locomotor parameters of four Swinhoe’s striped squirrels. The small-bodied arboreal mammals exhibit brief bouts of rapid asymmetric gaits. Spatio-temporal parameters on runways with experimentally varied dimensions of the setup enclosure were compared to test for their potentially confounding effects. We applied principal component analysis to evaluate changes to the overall locomotor pattern. A common, non-hierarchical, pooled statistical analysis of the data revealed significant differences in some of the parameters depending on enclosure dimensions. In contrast, we used a hierarchical Bayesian generalized linear model (GLM) that considers subject specific differences and population effects to compare the effect of enclosure dimensions on the measured parameters and the principal components. None of the population effects were confirmed by the hierarchical GLM. The confounding effect of a single subject that deviates in its locomotor behavior is potentially bigger than the influence of the experimental variation in enclosure dimensions. Our findings justify the common practice of researchers to intuitively select an enclosure with dimensions assumed as “non-constraining”. Hierarchical models can easily be designed to cope with limited sample size and bias introduced by deviating behavior of individuals. When limited data is available—a typical restriction of in-vivo motion analyses of non-model organisms—density distributions of the Bayesian GLM used here remain reliable and the hierarchical structure of the model optimally exploits all available information. We provide code to be adjusted to other research questions.

Whisker touch sensing guides locomotion in small, quadrupedal mammals.

All small mammals have prominent facial whiskers that they employ as tactile sensors to guide navigation and foraging in complex habitats. Nocturnal, arboreal mammals tend to have the longest and most densely packed whiskers, and semi-aquatic mammals have the most sensitive. Here we present evidence to indicate that many small mammals use their whiskers to tactually guide safe foot positioning. Specifically, in 11, small, non-flying mammal species, we demonstrate that forepaw placement always falls within the ground contact zone of the whisker field and that forepaw width is always smaller than whisker span. We also demonstrate commonalities of whisker scanning movements (whisking) and elements of active control, associated with increasing contact with objects of interest, across multiple small mammal species that have previously only been shown in common laboratory animals. Overall, we propose that guiding locomotion, alongside environment exploration, is a common function of whisker touch sensing in small, quadrupedal mammals.

The first tetrapod from the mid-Miocene Clarkia lagerstätte (Idaho, USA).

The Clarkia lagerstätte (Latah Formation) of Idaho is well known for its beautifully preserved plant fossils as well as a fauna of insects and fish. Here we present the first known tetrapod fossil from these deposits. This specimen, recovered from the lower anoxic zone of the beds, is preserved as a carbonaceous film of a partial skeleton associated with a partial lower incisor and some tooth fragments. The morphology of the teeth indicates that the first tetrapod reported from Clarkia is a rodent. Its skeletal morphology as well as its bunodont and brachydont dentition suggests that it is a member of the squirrel family (Sciuridae). It is a large specimen that cannot be assigned to a known genus. Instead, it appears to represent the first occurrence of a new taxon with particularly gracile postcranial morphology likely indicative of an arboreal ecology. This new specimen is a rare glimpse into the poorly known arboreal mammal fossil record of the Neogene. It supports a greater taxonomic and ecological diversity of Miocene Sciuridae than previously recognized and offers new lines of inquiry in the paleoecological research enabled by the unique preservation conditions of the Clarkia biota.

Landscape resistance influences effective dispersal of endangered golden lion tamarins within the Atlantic Forest

Habitat fragmentation threatens tropical rainforests, which can significantly hinder dispersal in species such as arboreal primates. For conservation actions to be effective there must be an understanding of how landscape structure and biological traits shape dispersal. We assessed the effects of landscape, sex and population management (reintroductions and translocations) on gene flow of Leontopithecus rosalia, an endangered arboreal primate living in highly fragmented forests of Brazil. We genotyped 201 individuals using 14 microsatellite loci to answer three questions: (1) How far does L. rosalia disperse? (2) Is dispersal sex-biased? (3) What are the relative contributions of population management, distance, roads and landscape resistance to genetic kinship? We hypothesized that (1) gene flow decrease between more distant sites; (2) males disperse more than females; and (3) management and land-cover resistance (i.e. landscape resistance) are the variables that most influence genetic kinship. We found positive spatial population-structure up to 8 km. The spatial structure was similar between females and males suggesting that they equally contribute to gene flow. Management and landscape resistance best explained genetic kinship, showing that different land-cover types affect the dispersal at different degrees of landscape permeability. We advocate that maintaining more permeable landscapes is essential to ensure dispersal and gene flow of arboreal mammals. Conservation measures in tropical rainforests must take into account not only the habitat amount, but also the degree at which each land use – roads, urban areas, agriculture, pasture, isolated trees, and stepping stones – facilitates or impedes the species dispersal.

Long-term survival of trees retained for hollow-using fauna in partially harvested forest in Tasmania, Australia

Hollow-using fauna are thought to be particularly vulnerable to timber harvesting, and habitat for these species is often managed by retaining single hollow-bearing trees or patches of hollow-bearing trees within the harvested area. This study examined tree retention, survival and use by arboreal mammals in 27 small clumps of trees (0.04–0.21 ha) retained at ten partial harvest sites and 24 clumps of trees in nearby unharvested sites in Tasmania, Australia. Harvested sites were assessed on three occasions (1999, 2005–06 and 2014) and unharvested sites on two occasions (2005–06 and 2014). Of the retained clumps in harvested areas, 96% contained at least two habitat trees at the time of first survey (one year after harvest) which is the minimum required under the Tasmanian Forest Practices Code. Loss of retained trees in clumps between 2005–06 and 2014 was higher in harvested sites (average of 11.7% of all trees and 1.5% of habitat trees per clump) than unharvested sites (average of 2.8% of all trees and 0.3% of habitat trees per clump), but was comparable to or lower than rates of loss in many other studies. Trees were more likely to fall if they were dead and had little burn damage at the time of last survey. Factors found to influence tree death included the interaction between burn damage and the size of the tree, with the likelihood of a heavily burnt, average sized tree dying being twice that of an unburnt tree. Scratch marks from arboreal mammals were more prevalent in large trees with visible hollows, particularly in the clumps in harvested areas. In conclusion, the Tasmanian Forest Practices Code provisions were generally implemented as required and the evidence suggests the retained clumps of trees survive and are effective to some degree at providing habitat and promoting recolonisation by fauna in partial harvest coupes. However, further work is required to assess the adequacy of the clump provisions, when combined with management for other values in production forests, for maintaining hollow-using fauna throughout their range.

Cyclones, fire, and termites: The drivers of tree hollow abundance in northern Australia’s mesic tropical savanna

Tree hollows are a vital wildlife feature, whose abundance and availability has declined in many regions due to broad-scale vegetation clearance, timber-harvesting, and disturbance such as fire. In the temperate forests and woodlands of eastern and southern Australia, the loss of large, old trees and associated tree hollows has severely impacted populations of hollow-dependent fauna. In the tropical savannas of northern Australia, many hollow-dependent mammals are in decline, and habitat simplification and resultant hollow limitation have been suggested as potential contributors to these declines. Hence, we sought to quantify the abundance of hollows, and identify the key drivers of this abundance in northern Australian savannas. We modelled the environmental and ecological correlates of hollow abundance across an extensive area of eucalypt savanna in Australia’s Northern Territory. We found that hollow abundance was significantly related to tree characteristics (size, species) and broad environmental gradients (annual rainfall, soil depth). Key disturbances – cyclones, fire, and termites – substantially disrupted these relationships and led to high variation in hollow abundance, even at a local scale. Hollow abundance across the study area was high by both Australian and global standards (hollows >5 cm entrance diameter: 88 ha–1, hollows >10 cm: 23 ha–1) and greatest in high rainfall areas (associated with the abundance of large eucalypts). Many arboreal mammal species in northern Australia have now contracted to higher rainfall parts of their former range (where hollows are at highest density); however such higher rainfall areas are also more likely to be affected by stochastic cyclonic events that can severely reduce the abundance of hollows. Hollow abundance was also affected by recent fire history and, in many areas, the current regime of frequent, high intensity fires will lead to marked reduction in this resource.

Gibbons (Nomascus gabriellae) provide key seed dispersal for the Pacific walnut (Dracontomelon dao), in Asia's lowland tropical forest

Understanding the mutualisms between frugivores and plants is essential for developing successful forest management and conservation strategies, especially in tropical rainforests where the majority of plants are dispersed by animals. Gibbons are among the most effective seed dispersers in South East Asia's tropical forests, but are also one of the highly threatened arboreal mammals in the region. Here we studied the seed dispersal of the Pacific walnut (Dracontomelon dao), a canopy tree which produces fruit that are common in the diet of the endangered southern yellow-cheeked crested gibbon (Nomascus gabriellae). We found that gibbons were the most effective disperser for this species; they consumed approximately 45% of the fruit crop, which was four times more than that consumed by macaques – the only other legitimate disperser. Gibbons tracked the temporal (but not spatial) abundance of ripe fruits, indicating this fruit was a preferred species for the gibbon. Both gibbons and macaques dispersed the majority (>90%) of the seeds at least 20 m away from parent crowns, with mean dispersal distances by gibbons measuring 179.3 ± 98.0 m (range: 4–425 m). Seeds defecated by gibbons germinated quicker and at greater rates than seeds spat by macaques, or in undispersed fruits. Gibbon-dispersed seeds were also more likely to be removed by unknown seed predators or unknown secondary dispersers. Overall, gibbons play a key role in the regeneration of the Pacific walnut. Our findings have significant implications both for the management of the Pacific walnut tree dominating tropical rainforest as well as the reintroduction program of the Southern yellow-cheeked crested gibbon.